Method for monitoring an amount of heavy metal contamination in a wafer

ABSTRACT

In order to monitor the amount of heavy metal contamination on a semiconductor wafer, the thickness of a monitor wafer is made smaller than a prescribed standard thickness with respect to the wafer diameter.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a wafer for a heavy metalmonitor and a method for manufacturing such a wafer, and moreparticularly to a method for manufacturing a wafer which is capable ofmeasuring the degree of heavy metal contamination with good accuracy,even in a manufacturing process in which a large-diameter wafer of 8inches or 12 inches and over is being processed, and to a method formanufacturing such a wafer.

[0003] 2. Description of the Related Art

[0004] In the past, in a process for manufacturing a semiconductor,heavy metal contamination, which causes a deterioration of thecharacteristics of a semiconductor, such as with regard to leakage, wasmeasured and monitored by a minority carrier lifetime measurementapparatus which made use of the μ-PCD method (microwave photoconductivedecay).

[0005] In particular, because it was advantageous to have the wafer thatis used for this monitoring be the same size as the wafer beingprocessed, as the size of silicon wafers grew, in order to achieverigidity with respect to stress, the thickness of the wafer grew large,the result being that the apparent lifetime became long, this hinderingmeasurement with good accuracy.

[0006]FIG. 3 shows the method of manufacturing a wafer used for heavymetal monitoring in the past. This wafer is subjected to thermaloxidation at a temperature in the range from 900° C. to 1000° C. in anatmosphere of O₂ or in an atmosphere of N₂ and O₂, thereby achievingthermal treating for the purpose of preventing surface recombination.

[0007] However, a metal such as titanium, which has a low diffusioncoefficient, is introduced into the oxide film during thermal treating,in which case there is a further deterioration of the measurementaccuracy.

[0008] Accordingly, it is an object of the present invention to improveon the drawbacks of the prior as noted above, by providing a novel waferwhich enables measurement of the amount of heavy metal contaminationwith good accuracy, even in a process of manufacturing a large-diameterwafer, and a further object to provide a method for manufacturing such amonitoring wafer.

[0009] Another object of the present invention is to provide a novelmethod for manufacturing a wafer for monitoring heavy metalcontamination that is capable of measuring of the amount of metalcontamination with good accuracy, while suppressing the measurementerror that is introduced by the introduction of a metal such astitanium, which has a low diffusion coefficient, into the oxide film.

SUMMARY OF THE INVENTION

[0010] In order to achieve the above-noted objects, the presentinvention adopts the following basic technical constitution.

[0011] Specifically, the first aspect of the present invention is awafer for heavy metal monitoring, said wafer having, for monitoring anamount of heavy metal contamination in a wafer, a thickness thereof thatis less than a prescribed standard wafer thickness as defined withrespect to the wafer diameter.

[0012] In the second aspect of the present invention, the thickness ofthe wafer is in the range from 250 μm to 750 μm.

[0013] In the third aspect of the present invention, in order to monitorheavy metal contamination in a wafer, heavy metal monitoring region isprovided on the wafer, the thickness of the wafer in this region beingless than a prescribed standard wafer thickness as defined with respectto the wafer diameter.

[0014] In the fourth aspect of the present invention, the heavy metalmonitoring region is provided in the approximate center part of thewafer.

[0015] In the fifth aspect of the present invention, the thickness ofthe heavy metal monitoring region is in the range from 250 μm to 750 μm.

[0016] The first aspect of a method for manufacturing a wafer is amethod for manufacturing a wafer for monitoring the heavy metalcontamination on a wafer, this method comprising;

[0017] a first step of thermal treatment to the wafer at a temperaturein the range from 1150° C. to 1350° C. in an atmosphere of O₂+He or anatmosphere of H₂+He, and

[0018] a second step of thermal treatment to the wafer at a temperaturein the range from 900° C. to 1000° C. in an atmosphere of N₂+O₂ or anatmosphere of O₂.

[0019] In the second aspect of a method for manufacturing a wafer forheavy metal contamination monitoring, the thickness of the wafer is lessthan a prescribed standard wafer thickness as defined with respect tothe wafer diameter.

[0020] In order to monitor the amount of heavy metal contamination on awafer, a wafer for heavy metal monitoring according to the presentinvention has a thickness thereof that is less than a prescribedstandard wafer thickness as defined with respect to the wafer diameter,and is capable of measuring the amount of heavy metal contamination withgood accuracy, with reduced measurement error.

[0021] A method of manufacturing a wafer for monitoring the amount ofheavy metal contamination on a wafer, by measuring minority carrierslifetime, this method having a first step of thermal treatment at atemperature in the range from 1150° C. to 1350° C. in an inert lightelement gas atmosphere of O₂+He or an atmosphere of H₂+He, and a secondstep of thermal treatment at a temperature in the range from 900° C. to1000° C. in an atmosphere of N₂+O₂ or an atmosphere of O₂, and by meansof these steps, it is possible to eliminate the measurement error thatoccurs because of the inclusion of a metal such as titanium, which has alow diffusion coefficient, into the oxide film during thermal treating,thereby resulting in the achievement of good measurement accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a drawing that shows a monitor wafer according to thepresent invention, with FIG. 1(a) being a cross-section view of thewafer, showing the first embodiment, and FIG. 1(b) being a plan view ofa wafer, showing the second embodiment.

[0023]FIG. 2 is a drawing that shows the manufacturing processes for themain part of a monitor wafer according to the present invention.

[0024]FIG. 3 is a drawing that shows the manufacturing processes for amonitor wafer of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Embodiments of a wafer for heavy metal monitoring according tothe present invention are described in detail below, with referencesbeing made to relevant accompanying drawings.

[0026]FIG. 1(a) is a drawing that shows the structure of an example of awafer for heavy metal monitoring according to the present invention,with FIG. 1(a) showing a wafer for heavy metal monitoring, wherein forthe purpose of monitoring the amount of heavy metal contamination on awafer, the thickness t of a wafer 1 is made smaller than a prescribedstandard wafer thickness T with respect to the wafer diameter.

[0027] In the manufacturing processes for manufacturing a semiconductorintegrated circuit, in the case in which the microwave photoconductivedecay method is employed to monitor, by measuring the minority carrierlifetime, the amount of heavy metals, which cause deterioration of thetransistor characteristics such as with regard to leakage, whereas inthe method of the prior art a heavy metal monitor wafer having astandard thickness (725 μm for an 8-inch wafer, 775 μm for a 12-inchwafer), in the case of the present invention a wafer having a thicknessin the range from 250 μm to 700 μm is used.

[0028] In the above-noted case, at below 250 μm, problems arise in thetransport of the wafer, for example, due to sag of the wafer because ofits thinness. Specifically, it had been advantageous to use a waferhaving the same thickness as a 6-inch wafer.

[0029] It has been theoretically and experimentally determined that theminority carrier lifetime that is obtained using the microwave PCDmethod is lengthened in proportion to the square of the wafer thickness,so that for a given heavy metal contamination level, the apparentlifetime is lengthened. Because of this, the present invention makes thewafer thickness 675 μm, so that it is possible to maintain a correctcorrelation between the sensitivity coefficient and the heavy metalcontamination amount.

[0030]FIG. 2 is a flowchart that shows the method for manufacturing aheavy metal monitor wafer according to the present invention, thisdrawing showing a method for manufacturing a wafer for monitoring heavymetals contamination in a wafer by measuring minority carrier lifetime,the method including a first step of thermal treatment to the wafer at atemperature in the range from 1150° C. to 1350° C. in an atmosphere ofO₂+He or an atmosphere of H₂+He, and a second step of thermal treatmentto the wafer at a temperature in the range from 900° C. to 1000° C. inan atmosphere of N₂+O₂ or an atmosphere of O₂.

[0031] Specifically, in the present invention, in order to prevent asmuch as possible the intrusion of the heavy metal such as titanium,which has a low diffusion coefficient with respect to silicon, into anoxide film, before the above-noted thermal treating, the temperature isset in the range from 1150° C. to 1350° C., and to eliminate errors thatoccur in the minority carrier lifetime because of crystal defects, athermal treating step is provided which is performed in an inert lightelement gas atmosphere of H₂ or He.

[0032] By virtue of the above-noted constitution, it is possible tosuppress the deterioration of the sensitivity coefficient that is causedby inclusion of a metal such as titanium into the oxide film that isformed during thermal oxidation that is performed for the purpose ofpreventing surface recombination, and it is also possible to eliminatethe cause of errors in lifetime decay due to crystal defects.

[0033]FIG. 1(b) is a drawing that shows the structure of anotherembodiment of a wafer for heavy metal monitoring, and FIG. 1(b) shows aheavy metal monitoring wafer in which a heavy metal monitoring region 3is provided on a wafer 2, the thickness t of this heavy metal monitoringregion 3 being less than a prescribed standard wafer thickness T withrespect to the diameter of the wafer 2.

[0034] In the past, when the monitor carrier lifetime measurement methodwas used to monitor heavy metal contamination during the manufacturingprocess, bare silicon having the standard thickness was used formeasurement of the lifetime. In the present invention, however, in orderto achieve a high sensitivity in the measurement of lifetimecommensurate with advances in the manufacturing processes, a chip forthe purpose of monitoring lifetime is provided in a thin part having athickness of 675 μm at the region 3 in the center part of the wafer.

[0035] Of course, the thickness in the above-noted region 3 in thecenter part can be set in the range from 250 μm to 700 μm, and thisregion does not absolutely need to be provided in the center part of thewafer.

[0036] In the present invention, the thickness of the wafer used formonitoring is established so as to be 675 μm, which is less than thestandard wafer thickness, this type of wafer being used to performlifetime measurement, thereby enabling the maintenance of a correctlycorrelated sensitivity coefficient, obtained from the correlationbetween the heavy metal contamination amount and the lifetime value,thereby enabling an improvement in measurement accuracy.

What is claimed is:
 1. A wafer for heavy metal monitoring, said waferhaving, for monitoring an amount of heavy metal contamination in awafer, a thickness thereof that is less than a prescribed standard waferthickness as defined with respect to the wafer diameter.
 2. A wafer forheavy metal monitoring according to claim 1, wherein the said waferthickness is in the range from 250 μm to 700 μm.
 3. A wafer for heavymetal monitoring, said wafer having, for monitoring an amount of heavymetal contamination in a wafer, a region thereon for heavy metalmonitoring, the wafer thickness of said region being less than aprescribed standard wafer thickness as defined with respect to the waferdiameter.
 4. A wafer for heavy metal monitoring according to claim 3,wherein said region for heavy metal monitoring is disposed in theapproximate center of said wafer.
 5. A wafer for heavy metal monitoringaccording to claim 3, wherein the thickness of said region for heavymetal monitoring is in the range from 250 μm to 700 μm.
 6. A method formanufacturing a wafer for monitoring heavy metal contamination amount bymeasuring minority carrier lifetime, said method comprising: a firststep of thermal treatment to said wafer at a temperature in the rangefrom 1150° C. to 1350° C. in an atmosphere of O₂+He or an atmosphere ofH₂+He, and a second step of thermal treatment to said wafer at atemperature in the range from 900° C. to 1000° C. in an atmosphere ofN₂+O₂ or an atmosphere of O₂.
 7. A method for manufacturing a wafer forheavy metal monitoring according to claim 6, wherein the thickness ofsaid wafer is less than a prescribed standard wafer thickness as definedwith respect to the wafer diameter.